1. Field of the Invention
The present invention relates to a process for the preparation of an N-(.alpha.-alkoxyethyl)carboxylic acid amide, which is an intermediate leading to an N-vinylcarboxylic acid amide which can be utilized as the material for the synthesis of polyvinylamine as a water-soluble polymer, and chemicals such as taurine and cysteamine. More particularly, the present invention relates to a process for preparing an N-(.alpha.-alkoxyethyl)carboxylic acid amide by reacting an ethylidene-bisamide with an alkanol in the presence of an acid catalyst.
2. Description of the Related Art
Various processes for the synthesis of an N-(.alpha.-alkoxyethyl)carboxylic acid amide have been proposed. For example, the following processes can be mentioned.
(a) Japanese Unexamined Patent Publication No. 50-76014 discloses a process in which N-acyl-.alpha.-alanine is subjected to electrolytic oxidation in an alcoholic solvent to effect decarboxylation and alkoxylation.
(b) Japanese Unexamined Patent Publication No. 55-154589 discloses a process in which an N-ethylcarboxylic acid amide is subjected to electrolytic oxidation in an alcoholic solvent to effect alkoxylation.
(c) Japanese Unexamined Patent Publication No. 56-75464 discloses a process in which an .alpha.-halogenoalkyl ether is reacted with a carboxylic acid amide in the presence of a tertiary amine.
(d) The specification of U.S. Pat. No. 4,554,377 discloses a process in which dimethylacetal is reacted with a carboxylic acid amide in the presence of an acid catalyst.
(e) Japanese Unexamined Patent Publication No. 60-149551 discloses a process in which an N-(.alpha.-alkoxyethyl)carboxylic acid amide is prepared through N-(.alpha.-hydroxyethyl)formamide obtained from formamide and acetaldehyde.
All of these known processes however, have serious disadvantages. For example, the processes (a) and (b) are disadvantageous in that the starting N-acyl-.alpha.-alanine and N-ethylcarboxylic acid amide are expensive, production is difficult because an electrochemical method is used, and a problem arises in the maintenance and control of an electrolytic cell and electrodes.
In the process (c), for the synthesis of the starting .alpha.-halogenoalkyl ether, a hydrogen halide must be used in an amount equimolar to the starting aldehyde.
The process (d) is defective in that dimethylacetal must be separately synthesized, and be once isolated and used. In the process (e), the starting carboxylic acid amide is limited to formamide giving a relatively stable N-(.alpha.-hydroxyethyl) compound.
For example, N-(.alpha.-hydroxyethyl)acetamide which is the intermediate formed when acetamide is used as the starting compound is an unstable compound, and isolation of this compound is impossible. The same reaction that occurs when formamide is used, cannot be advanced.
As apparent from the foregoing description, none of the conventional processes for the synthesis of an N-(.alpha.-alkoxyethyl)carboxylic acid amide can be regarded as widely-applicable and simple process.
As the process for industrially advantageously preparing an N-(.alpha.-alkoxyethyl)carboxylic acid amide while solving the problems of these conventional processes, the present inventors proposed a process comprising reacting three easily available and cheap compounds, i.e., a carboxylic acid amide, acetaldehyde, and an alcohol, in one state in the presence of a strongly acidic or weakly acidic cation-exchange resin, to synthesize an N-(.alpha.-alkoxyethyl)carboxylic acid amide at a high yield [see Japanese Unexamined Patent Publication No. 62-289549 (Laid-open on Dec. 16, 1987) and Japanese Unexamined Patent Publication No. 63-96160 (Laid-open on Apr. 27, 1988)].
According to this process, the intended N-(.alpha.-alkoxyethyl)carboxylic acid amide can be obtained at a high yield in one stage by using three easily available starting materials, and cumbersome post treatments such as a separation of the catalyst are not necessary. According to this process, the intended N-(.alpha.-alkoxyethyl)carboxylic acid can be simply obtained at a high yield, but the acetaldehyde and alcohol must be used in excessive amounts relative to the carboxylic acid amide and the acetaldehyde and alcohol must be recovered after the reaction and reused.